Electron device



June 21, 1932. c; G. SMITH ELECTRON DEVICE Filed March 22, 1928 Patented June 2i, 1932 UNITED sTATEsrA ENT OFFICE.

CHARLES G. SMITH, OF MEDFOBD, HASSACHUSETTS, ASSIGNOR TO RAYTHEON ING, OF CAMBRIDGE, MASSACHUSETTS, A CORPORATION: OF MASSACHUSETTS ELECTRON DEVICE Application filed larch 22, 1928. serial No. 268,699.

My present invention relates generally to thermionic devices and in particular to the type which employs gas or vapor to facilitate conduction although not restricted to that type and has application \to various uses such as amplification ofelectric current and detection of radio signals.

An object of m invention is to rovide a new and improve tube structure 0 the type mentioned which is more eflicient than those heretofore employed.

The novel features which I believe characteristic of my invention are set forth with particularity in the appended claims.- The lnvention itself, however, both as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following description taken in connection with the accompanying drawing in which the figure represents a preferred embodiment.

As indicated on the drawing I employ a heater element 1 in the form of a filament, a cylindrical cathode 2, a control element 3 and an anode or plate electrode 4 of cylindrical form, concentrically arranged and all supported in the usual manner from the ress of an envelope 5 from which the air has een completel excluded. The cathode consists of a thim le made of a material, refractory and having a relatively large heat capacity and practically surrounds the filament so that it may be heated readily by radiation. The thimble supports the lower end of the filament in the manner shown and provides a terminal therefor. The upper portion of the thimble is extended radially as a web or other conducting body, terminating in an intersticed member 6 whichmay be a helix, positioned between the control electrode 3 and anode 4.

For reason stated hereinafter, the distance between the member 6 and anode should be relatively small. The control electrode -3 may take any form but I find it desirable to give it a shape conforming to that of member 6 i. e. helical. In order to facilitate conduction, a vapor or an inert gas may be present within the envelope at a relatively low pressure; caesium vapor at a pressure approximately 10- mm. Hg has given satisfactory results and may be admitted by heating capsule 7 which containssuitable chemical e. g. caesium chloride and calcium chips. By spacing the portion 6 of the cathode a relatively short distance away from the plate 4, ionization by collision of electrons with caesium molecules is minimized. The theory upon which this is based is set out in my Patent 1,545,207 granted July 7, 1925, and later patents;

In operation, the electrodes are connected to input and output circuits in the usual manner for signal amplification or detection, except that an additional lead is provided for the upper end of the filament which may be energized by alternating or direct current of suitable voltage; when alternating current is utilized, the metal content of the thimble is suflicient to maintain a substantially constant temperature durin the whole of the alternating current'cycle. *manations from the filament render the thimble portion 2 of the cathode electronically active which then takes on the function of a cathode. If desired, the thimble may be treated with material designed to increase electron emission e. g. by

- coating with alkaline earth metal oxide or intermixing same with the metal content; although if caesium is employed for the-vapor it will inevitably settle upon all the metal parts of the .tube including the outer surface of the thimble and suffice for this purpose. The position of the thimble is such that it prevents the light radiation of filament from passing directly to the space bounded'by the remaining electrodes, hence, photoionization of the conducting medium in the neighborhood of grid 3 is precluded, which is appreciable in the case of caesium, and the grid remains unheated. This, in addition to the presence of the relatively short space between member 6 and thepla-te over which any appreciable voltage exists, enables the grid element to exercise a most effective control, in fact, quite as much as in any ordinary electronic device. By placing a portion of the cathode member intermediate the grid and plate, feed-back and grid to plate capacity is diminished since'the grid is shielded from electrostatic action of the plate; the same shielding action also assures amplification greater than is ordinarily found in the usual type of tube.

I claim: a a

1. An electron dischargedevicecom rising an evacuated envelope, a thermionical y emittin cathode and an anode supported in sai envelope, a control grid between said cathode and said anode, and an additional grid conductively connected to and mechanically supported by said cathode between said control grid and said anode.

2. An electron discharge device comprising an evacuated envelope, a pair of tubular 616C? trode members surrounding eachotherwithin said envelope, means supportingone of said members in the envelope, means mechanical- 1y supporting the other of said members from said first member, an anode in said envelope, one of said members constituting an electronemitting cathode, the other of said members having perforations to permit passage of electrons therethrough to said anode, and a control grid between said two members.

3. An electron discharge device com rising an evacuated envelope, a tubular ca ode member supported in said envelope, a grid surroundin said cathode and carried thereby, said grid being conductively connected to said cathode, an anode surrounding said grid, an additional control grid interposed between said first grid and said cathode, and an incandescible heater inside said tubular cathode member, said cathode member bein g positioned to screen the sp'acebetweensaid cathode and said anode from irradiation by said incandescible member.

4. An electron discharge device comprising an evacuated envelope, a tubular cathode supported in said envelope, a grid surrounding said cathode and connected thereto, an anode surrounding said grid, a control grid interposed between said first grid and said cathode, an easily ionizable gas filling in said envelope, and an incandescible heater inside said cathode, said cathode being positioned to protect the gas filling in the discharge space heating the same to a temperature of electron being short to substantially reduce ionization of gas by collision with electrons moving through the dischar e space underrthe action of the field between e anode and the cathode.

In testimony whereof, I have signed my name to this specification.

' CHARLES G. SMITH.

from ionization through irradiation by said v incandescible heater, the spacing between said first grid and said anode being short to substantially reduce ionization of gas molecules by electrons moving through the space under the action of the field between the anode and the cathode.

5. An electron discharge device comprising an evacuated envelope, a relatively large-surface cathode member, an anode facing one side of said cathode, a. protective grid interposed between said cathode and said anode, said grid being electrically connected to said cathode, a control grid between said protective grid and said'cathode, an easily ionizable gas filling in said envelope, and an incandescile heating element adjacent said cathode for 

